This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The Diagnostic and Statistical Manual of Mental Disorders (4th Edition) (DSM IV-TR 2000) classifies BPD as an Axis II Cluster B Personality Disorder. DSM IV criteria for BPD include affective instability, impulsive risk taking behavior, inappropriate and intense anger, unstable relationships that rapidly shift between idealization and devaluation, unstable self image, feelings of emptiness, dissociative experiences, self injurious behavior such as superficial skin cutting or burning, and multiple suicide attempts (DSM IV-TR 2000). The designation of BPD as an Axis II personality disorder reflects the historical conceptualization that personality disorders are psychologically and developmentally rooted, rather than biologically based and genetically determined such as the Axis I disorders. More recently, alternative conceptualizations of BPD and personality disorders have arisen, lending theoretical rationale for the use of medications in the treatment of BPD. The goal of this proposal is to determine the efficacy of intranasal oxytocin as a first-line monotherapy in the treatment of Borderline Personality Disorder (BPD), via a 6-week, randomized, placebo-controlled trial in 40 adult participants over a two year period. Hypothesis: Primary Treatment Hypothesis: 1. Oxytocin will be superior to placebo in treating global severity of BPD, as measured by the ZAN-BPD and the CGI-I. Secondary Treatment Hypotheses: 1. Oxytocin will be superior to placebo in other treatment outcome measures. 2. Oxytocin will be superior to placebo in improving functional disability, as measured by the Sheehan Disability Scale. Exploratory Hypothesis: 1. We will pilot the use of Event Contingent Recording (ECR) to assess changes in mood and social functioning over the course of treatment in adults with BPD in a naturalistic fashion. Challenge Hypotheses: 1. Oxytocin will be superior to placebo in enhancing emotional regulation and emotional processing capacity, as evidenced by the Emotion Regulation Task, the Attentional Bias to Acceptance/Rejection Task, and the Perception of Dynamic Emotion Expressions Task.